Hydraulic friction draft gear

ABSTRACT

A hydraulic friction draft gear having a movable hollow ram casing defining with an interior floating accumulator piston assembly a gas chamber which is charged with gas through the accumulator piston assembly.

United States Patent Carlson et al. 5] Feb. 1, 1972 [54] HYDRAULIC FRICTION DRAFT GEAR 3,240,355 3/1966 Karbowniczek ..2l3/43 [72] Inventors: Robert L. Carlson, Chicago; R0" A 3,266,792 8/1966 Shernll ....267/64 B Madland Palos Heights both of "L 3,232,599 2/1966 Faisandler ....267/64 B 3,412,870 11/1968 Rollins ..213/43 [73] Assignee: Miner Enterprises, Inc., Chicago, Ill.

22 Filed: Jan. 21 1970 Primary Examiner--Drayton E. Hoffman Attorney-Edward F. Jurow and Clifford A. Dean [2]] App]. No.: 4,663

[57] ABSTRACT 52 .S. l. ..21 22, 3 43, 7 64 a b 2 A hydraulic friction draft gear having a movable hollow ram [58] Fie'ld 43 267/64 casing defining with an interior floating accumulator piston a 267; 1 sembly a gas chamber which is charged with gas through the accumulator piston assembly. [56] References Cited 2 Claims, 3 Drawing Figures PATENTEB ma H912 SHEET 16? 2 EOEEET L. (AELSON ROLF A MAUI-4N0 I N VENTORS SHEET 2 OF 2 PATENTED FEB 1 I972 HYDRAULIC FRICTION DRAFT GEAR BACKGROUND OF THE INVENTION The present invention pertains generally to a hydraulic friction draft gear which may be used in the shock absorbing system of a railway car or the like.

Certain draft gears of this type have been provided with a chamber containing pressurized gas which compresses under draft gear loading and expands upon release of the load to return the draft gear elements to a normal position. In prior such arrangements, manufacture and assembly has been expensive, charging of the gas chamber has been inconvenient, undesirable gas leakage has been experienced, and frequent maintenance has been required.

SUMMARY OF THE INVENTION A draft gear incorporating the principles of the present invention comprises a housing, friction shoes at one end thereof, and a hydraulic unit interiorly thereof. The hydraulic unit includes a pressure tube, a hollow rarn casing having a closed end and an open end slidable in the pressure tube, a floating accumulator piston assembly slidable in the ram casing and defining therewith a gas chamber, and a ram piston assembly secured in the open end of the ram casing and defining with the accumulator piston assembly and pressure tube a pair of liquid chambers. A force or load applied to the draft gear is dissipated by friction at the shoes, and by metering of liquid between the pair of liquid chambers. During the dissipation of energy, gas within the gas chamber is compressed; upon release of the load, the gas expands to return the draft gear elements to a normal position.

With particular reference to the gas chamber, there is formed in the accumulator piston assembly an axial aperture through which gas is adapted to be admitted to charge the chamber, and a ball check valve is seated within the axial aperture for preventing the escape of gas after the chamber has been charged. With this arrangement, the initial gas charge is effected interiorly of the ram casing through the accumulator piston during assembly of the hydraulic unit, thereby simplifying and facilitating charging of the chamber. Moreover, fabrication and assembly of the unit, gas leakage therefrom, and maintenance thereof, are minimized.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal view, partly in elevation and partly in section, of a hydraulic friction draft gear incorporating the principles of the present invention;

FIG. 2 is an enlarged longitudinal view, partly in elevation and partly in section, of the ram section of the hydraulic unit incorporated in the draft gear of FIG. 1, and shows the ram section in an intermediate stage of assembly preliminary to charging the same with gas;

FIG. 3 is a transverse sectional view, taken substantially along the line 3-3 in FIG. 2, looking in the direction indicated by the arrows; and

FIG. 4 is a further enlarged view of the ram piston assembly screw utilized in the intermediate stage of assembly while the ram section of the hydraulic unit is being charged with gas.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, there is indicated generally by the reference numeral a hydraulic friction draft gear incorporating the principles of the present invention. The draft gear 10 includes a housing 12 of hexagonal cross section having a closed rearward end 14. The open forward end of the housing 12 is provided with tapered inner friction surfaces 16 and inwardly turned flangelike lugs 18. Disposed in the forward end of the housing 12 are three winglike friction shoes 20 which are provided with tapered external friction surfaces 22 that engage the housing friction surfaces 16 and which are further provided with inner tapered friction surfaces 24 that define a pocket for receiving the inner end of a wedge member 26. To

limit movement of the wedge member 26 and friction shoes 20 outwardly of the housing 12, the wedge member 26 is provided with outwardly projecting flangelike lugs 28 which, during assembly of the draft gear, are engaged inwardly of the lugs 18 of the housing 12. Seated against the inner ends of the friction shoes 20 is a follower plate 30.

Disposed within the housing 12 intermediate of the rearward end 14 and the follower plate 30 is a hydraulic unit indicated generally by the reference numeral 32. The hydraulic unit 32 comprises a pressure tube 34, a hollow ram casing 36, a floating accumulator piston assembly 38, and a ram piston assembly 40.

The pressure tube 34 includes a rearward wall 42 which is seated against the closed rearward end 14 of the housing 12 and which is provided with a central axial opening 44 having a removable filler plug 46 threaded therein. Slidable axially within the pressure tube 34 is the ram casing 36 which includes a solid closed forward wall 48 seated against the follower plate 30 and which is formed with circumferentially spaced radial passages 49 adjacent the rearward end thereof. lnterposed between the pressure tube 34 and the ram casing 36 are an annular seal 50, packing elements 52, and a gland unit 54.

The accumulator piston assembly 38, which is axially slidable within the ram casing 36, includes a piston 56 having a central axial aperture 58 therein. The aperture 58 is provided with an intermediate valve seat against which is normally seated a rubber ball check valve 60. A retainer ring 62 is mounted in the forward end of the axial aperture 58 for limiting movement of the ball check valve 60 within the piston 56, and removable seal means in the form of a screw 64 is threaded in the rearward end of the axial aperture 58. Carried at the outer periphery of the piston 56 and engageable with the inner periphery of the ram casing 36 are annular seals 66 and an intermediate Tshaped ring seal 68.

The ram piston assembly 40 includes a piston 70 threaded into the rearward end of the ram casing 36 and retained in position by a locking pin and set screw 72. A slight annular clearance 73 is maintained between the outer peripheries of the ram casing 36 and piston 70, and the inner periphery of the pressure tube 34. The piston 70 is formed with circumferentially spaced axial passages 74 communicating with an annular groove 76 in which is arranged a floating piston ring 78, and is also formed with circumferentially spaced axial metering holes 80 and a central axial bore 81. An annular valve disc 82 is biased into closure engagement with the inner ends of the piston holes 80 by means of disc springs 84. The valve disc 82 and the disc springs 84 are maintained in operative position by means of an annular retainer member 86 which is threadedly mounted on the inner end of an adjustment screw 88 projecting through the piston bore 81.

The accumulator piston assembly 38 defines with the ram casing 36 a gas chamber 90; the ram piston assembly 40 defines with the accumulator piston assembly 38 and ram casing 36 a first liquid chamber 92, and defines with the pressure tube 34 a second liquid chamber 94. Preferably, the gas chamber 90 is charged with nitrogen gas, and the first and second liquid chambers 92 and 94 are filled with hydraulic fluid or oil.

Operationally, the pressure at which the valve disc 82 is moved away from the piston holes 80 for opening the same to accommodate metering of hydraulic fluid from the chamber 94 to the chamber 92, and correspondingly the degree of stiffness of the draft gear, is dependent upon the torque setting applied to the adjustment screw 88.

One of the principal features of the draft gear 10 resides in the construction of the accumulator piston assembly 38 and the manner in which the chamber 90 is charged with nitrogen gas. Referring now to FIGS. 2-4, in assembly of the draft gear 10, the accumulator piston assembly 38 (without the seal screw 64) is first inserted in the ram casing 36, and the ram piston assembly 40 is then secured in the rearward end of the ram casing 36. During the latter assembly operation, a special assembly screw 96 having a central axial opening 98 therethrough is temporarily mounted in the ram piston bore 81 in place of the regular adjustment screw 88. A charging tube 100, which is suitably connected to a source of nitrogen under pressure, is inserted through the assembly screw opening 98 and threaded into the accumulator piston 56. As nitrogen gas is directed through the charging tube 100, the ball check valve 60 is unseated, and the gas is permitted to flow into the chamber 90 whereby the same is charged. While the chamber 90 is being charged with nitrogen gas, the accumulator piston assembly 38 moves rearwardly within the ram casing 36 and eventually bottoms out against the valve disc 82. After the chamber 90 has been charged with gas to a pressure of about 400 psi, the charging tube is removed, while the ball check valve 60 reseats to prevent the escape of gas through the charging aperture 58. Next, referring again to FIG. 1, the seal screw 64 is tightened in place, the special assembly screw 96 is replaced by the regular adjustment screw 88, and the proper torque is applied to the screw 88 for the desired stiffness of the draft gear. The entire piston ram assembly is then inserted into the pressure tube 34, the packing elements 52 and gland unit 54 are assembled, the hydraulic unit is extended to the proper free length, hydraulic fluid is introduced through the pressure tube opening 44 into the hydraulic unit, and the filler plug 46 is secured in the opening 44. The resultant hydraulic unit, together with the follower plate 30, the friction shoes 20, and the wedge member 26, is mounted during the final assembly step in the draft gear housing 12.

By arranging for the charge of the chamber 90 to be effected interiorly of the ram casing 36, a solid closed forward wall 48 may be utilized. With the foregoing arrangement, gas leakage from the forward end of the ram casing 36 is prevented by the closed wall 48, gas leakage through the piston aperture 58 is prevented by the ball check valve 60, and gas leakage past the piston 56 is substantially prevented or minimized by the seals 66 and 68. Under static conditions, the hydraulic fluid in the chamber 92 is at the same pressure as the nitrogen gas in the chamber 90; hence the accumulator piston assembly 38 is in balance, and there is no pressure differential to cause a flow of gas past the seals 66 and 68. Under dynamic conditions, although there .is a slight pressure differential across the accumulator piston assembly 38 due primarily to the inertia of the latter, the seal 68 serves to prevent gas leakage therepast. The screw 64 serves as additional seal means to prevent the passage of fluid through the piston aperture 58 in either direction between the chambers 90 and 92.

In the operation of the hydraulic friction draft gear 10, impact forces or loads imposed thereon cause the wedge member 26, friction shoes and follower plate 30 to move inwardly of the housing 12 whereby the ram casing 36 and ram piston assembly 40 are urged rearwardly. As rearward movement of the ram piston assembly 40 commences, pressure initially built up in the hydraulic fluid within the second liquid chamber 94 causes the floating piston ring 78 to be forced into abutment with the forward side of the annular groove 76 thereby preventing hydraulic fluid from flowing through the annular clearance 73. Concurrently, the pressure of the hydraulic fluid within the second liquid chamber 94 increases to a point where the valve disc 82 is unseated from the piston holes 80 against the load of the disc springs 84, whereupon hydraulic fluid flows from the second liquid chamber 94 through the piston holes 80 to the first liquid chamber 92. in this manner, the energy of the impact forces is dissipated by friction at the friction surfaces 22 and 24, and by metering of the hydraulic fluid between the pair of chambers 92 and 94. Also, the displacement of hydraulic fluid into the first liquid chamber 92 causes the accumulator piston assembly 38 to move forwardly relative to the ram casing 36 thereby compressing the nitrogen gas in the gas chamber and increasing its pressure.

When the impact forces are removed from the hydraulic friction draft gear 10, the ressure of the hydraulic fluid in the second liquid chamber 9 decreases, and the pressure of the nitrogen gas in the gas chamber 90 forces the accumulator piston assembly 38 rearwardly relative to the ram casing 36. At the same time, the floating piston ring 78 moves into abutment with the rearward side of the annular groove 76 thereby permitting the flow of hydraulic fluid from the first liquid chamber 92 to the second liquid chamber 94 through the casing passages 49, the annular clearance 73, the annular groove 76 and the piston passages 74. In this manner, the nitrogen gas serves, like a spring, to return the accumulator piston assembly 38, the ram casing 36, and, in turn, the follower plate 30, the friction shoes 20 and the wedge member 26, to the normal rest position shown in FIG. 1.

While there has been shown and described a preferred embodiment of the present invention, it will be understood by those skilled in the art that various rearrangements and modifications may be made therein without departing from the spirit and scope of the invention.

We claim:

1. For use in a friction draft gear of the type including an elongated housing having a closed rearward end and an open forward end which is provided with internal tapered friction surfaces, friction shoes at the open end of the housing and engaging the friction surfaces, a follower plate seated against the inner ends of the friction shoes, and a wedge member engaging the friction shoes and arranged for actuating the same upon movement thereof inwardly of the housing, the combination of a hydraulic unit comprising a pressure tube within said housing and having a closed rearward wall seated against said closed rearward end of said housing, a hollow ram casing slidable axially in said pressure tube and having a sealingly closed forward wall seated against said follower plate, a free floating accumulator piston assembly axially slidable in said ram casing and defining with said closed forward Wall thereof a gas chamber, a ram piston assembly secured in the rearward end of said ram casing, said ram piston assembly defining with said accumulator piston assembly a first liquid chamber and defining with said closed rearward wall of said pressure tube a second liquid chamber, said accumulator piston, said ram piston assembly, and said closed rearward wall of said pressure tube having aligned sealable axial pressure formed therein through which gas is adapted to be admitted to said gas chamber through a suitable elongated charging tube inserted through said aligned axial apertures for initially charging and recharging same, and a ball check valve seated within said axial aperture for preventing the passage of gas from said gas chamber into said first liquid chamber.

2. The combination of claim 1 including a threaded bore formed in the rearward end of said axial aperture of said free floating accumulator piston for threadedly receiving the threaded end of a suitable elongated charging tool during charging and recharging of said gas chamber and for threadedly receiving a seal screw after completion of such charging operations whereby to prevent the passage of fluid between said first liquid chamber and said gas chamber. 

1. For use in a friction draft gear of the type including an elongated housing having a closed rearward end and an open forward end which is provided with internal tapered friction surfaces, friction shoes at the open end of the housing and engaging the friction surfaces, a follower plate seated against the inner ends of the friction shoes, and a wedge member engaging the friction shoes and arranged for actuating the same upon movement thereof inwardly of the housing, the combination of a hydraulic unit comprising a pressure tube within said housing and having a closed rearward wall seated against said closed rearward end of said housing, a hollow ram casing slidable axially in said pressure tube and having a sealingly closed forward wall seated against said follower plate, a free-floating accumulator piston assembly axially slidable in said ram casing and defining with said closed forward wall thereof a gas chamber, a ram piston assembly secured in the rearward end of said ram casing, said ram piston assembly defining with said accumulator piston assembly a first liquid chamber and defining with said closed rearward wall of said pressure tube a second liquid chamber, said accumulator piston, said ram piston assembly, and said closed rearward wall of said pressure tube having aligned sealable axial pressure formed therein through which gas is adapted to be admitted to said gas chamber through a suitable elongated charging tube inserted through said aligned axial apertures for initially charging and recharging same, and a ball check valve seated within said axial aperture for preventing the passage of gas from said gas chamber into said first liquid chamber.
 2. The combination of claim 1 including a threaded bore formed in the rearward end of said axial aperture of said free-floating accumulator piston for threadedly receivIng the threaded end of a suitable elongated charging tool during charging and recharging of said gas chamber and for threadedly receiving a seal screw after completion of such charging operations whereby to prevent the passage of fluid between said first liquid chamber and said gas chamber. 